Electrospinning apparatus and electrospinning method

ABSTRACT

An electrospinning apparatus for the production of fibrous materials includes a compartment having at least one chamber to contain a substance from which fibers are to be formed. The chamber is electrically charged at a chamber potential. The apparatus also includes a collector to collect the fibers from the chamber. The collector is electrically charged at a ground potential different from the chamber potential, thereby establishing an electric field between the chamber and the collector. The chamber includes a forming layer having a plurality of openings through which the substance is extruded into the fibers.

The present invention relates to an electrospinning apparatus, particularly for the production of fibrous materials, and to an electrospinning method which uses said electrospinning apparatus.

Nowadays, there is a strong interest in developing materials based on microfibers, and more preferably based on nanofibers, that could be used in different fields such as medicine, textiles and military industry. Many potential applications for nanofibers are being developed as the ability to manufacture and control their chemical and physical properties improves.

Electrospinning is a fiber production method which uses an electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of nanometers. Electrospinning shares characteristics of both electrospraying and conventional dry spinning of fibers.

In particular, electrospinning is an atomization process of a conducting fluid (e.g., a semi-dilute polymer solution or a polymer melt) which exploits the interactions between an electrostatic field and the conducting fluid.

When an external electrostatic field is applied to the conducting fluid, a suspended conical droplet is formed, whereby the surface tension of the droplet is in equilibrium with the electric field. Electrostatic atomization occurs when the electrostatic field is strong enough to overcome the surface tension of the liquid. The liquid droplet then becomes unstable and a tiny jet is ejected from the surface of the droplet in the form of a fiber. As it reaches a grounded target, the material can be collected as an interconnected web containing fine fibers.

A basic electrospinning apparatus produces an electric field that guides the polymer solution or melt extruded from the tip of a needle, or nozzle, to an opposite collecting electrode. A reservoir connected to said needle, or nozzle, stores the polymer solution. The electric field is created between the tip of the needle, or nozzle, and the collecting electrode. Such electric field drives the polymer solution from the tip of the needle towards the collecting electrode. The polymer solution dries during the flight from the needle to the electrode, thus forming the polymeric fibers. The fibers are then collected downstream of the electrode where they can form films or membranes.

A variety of polymers can be used for electrospinning, such as nylon, fluoropolymers, polyolefins, polyimides, polyesters, and other engineering polymers or textile forming polymers.

Currently, in order to scale up the electrospinning fiber production, it is known to use multiple jet systems which comprise a plurality of electrified nozzles, either distributed along a line or over an area.

However, the known technology for electrospinning has nowadays still many limitations for large scale production of fibers and fibrous products, and in particular for large scale production of nanofibers and products constituted by nanofibers.

In case of an electrospinning apparatus with a plurality of electrified nozzles or needles, in fact, the complexity of the controls necessary to set and maintain the electrical field at each nozzle scales up with the number of said nozzles.

Furthermore the known technology does not allow to easily produce fibrous products, such as films and membranes, comprising several and different base materials, because the electrospinning of different polymer solutions or melts having different physical and chemical properties, through a plurality of nozzles, is very cumbersome and therefore very costly.

The aim of the present invention is to provide a an electrospinning apparatus, particularly for the production of fibrous materials, and an electrospinning method which solves the above drawbacks, by making it possible to scale up the industrial production of fibers and fibrous products, with particular regard to nanofibers and nanofiber products.

Within this aim, an object of the present invention is to provide an electrospinning apparatus and an electrospinning method which ameliorate the deficiencies of the known technology.

Another object of the invention is to provide an electrospinning apparatus and an electrospinning method which allow the processing of various kinds of polymer solutions and polymer melts, taking into account the different chemical and physical properties of such polymer solutions and melts.

A further object of the invention is to provide an electrospinning apparatus and an electrospinning method which allow to simultaneously extrude a plurality of fibers from different kinds of polymer solutions and polymer melts, to form complex and composite fibrous products.

A further object of the invention is to provide an electrospinning apparatus and an electrospinning method which are easy to implement and capable of offering the widest guarantees of reliability and safety in use.

A still further object of the invention is to provide an electrospinning apparatus the use of which entails an economic competitive advantage.

This aim and these and other objects which will become better apparent hereinafter are achieved by an electrospinning apparatus, particularly for the production of fibrous materials, according to claim 1. Furthermore this aim is also achieved by an electrospinning method according to claim 12.

Additional features are provided in the dependent claims.

Further characteristics and advantages of the invention will become better apparent from the detailed description of a preferred, but not exclusive, embodiment of an electrospinning apparatus, which is illustrated by way of a non-limiting example in the accompanying drawings wherein:

FIG. 1 is a schematic frontal view of an embodiment of the electrospinning apparatus, according to the invention;

FIG. 2 is a schematic bottom view of the electrospinning apparatus of FIG. 1, according to the invention.

With reference to the figures, the electrospinning apparatus, generally designated by the reference numeral 1, comprises:

-   -   a compartment 3 which comprises at least one chamber 5 adapted         to contain a substance from which fibers are to be formed,         wherein said at least one chamber 5 is electrically charged at a         chamber potential;     -   a collector 7 adapted to collect said fibers from the at least         one chamber 5, wherein said collector 7 is electrically charged         at a ground potential different from the chamber potential,         thereby establishing an electric field between the at least one         chamber 5 and the collector 7.

According to the invention, the at least one chamber 5 comprises a forming layer 9 comprising a plurality of openings 90 through which said substance is extruded into said fibers.

The forming layer 9 comprising the plurality of openings 90 allows to easily extrude a plurality of fibers from the substance contained in the chamber 5, thus overcoming the drawbacks of dealing with a plurality of needles or nozzles, which need to be singularly electrically charged.

Advantageously, the forming layer 9 is made of an electrically conductive material and it is electrically charged at said chamber potential.

For example, the forming layer 9 can be a net or a grid of a conductive material with a plurality of said openings 90. The use of a net of conductive material allows to accurately control the voltage applied to the forming layer 9, and thus the electrostatic field which spins the fibers from the chamber 5 to the collector 7.

Advantageously the forming layer 9 is provided at the bottom of the chamber 5, below the substance to be electrically spun.

Advantageously the compartment 3 lies vertically above the collector 7, so that the fibers being formed can fall onto the collector 7 also by means of the force of gravity.

Advantageously the at least one chamber 5 comprises heating and/or cooling means 11 configured to heat and/or cool the chamber 5, and therefore the substance contained in the chamber 5, to a desired temperature.

The thermoregulation of the chamber 5 allows to accurately control the viscosity of the substance contained in the chamber 5, since the viscosity of a fluid is highly temperature dependant.

The viscosity of the solution in the chamber 5 and the electrical field applied to the chamber 5 are two fundamental parameters to control the overcoming of the surface tension of the solution which faces the openings 90 of the forming layer 9. Therefore the high level of control of both the electrical field and the temperature of the chamber 5 allow a very fine tuning of the fiber electrospinning process.

The electrospinning apparatus 1 can comprise rotation means 13 configured to rotate the compartment 3 with respect to the direction of extrusion of the fibers, so that the fibers can be dispersed when electrospun and thus distributed on the collector 7.

According to a preferred embodiment, the compartment 3 comprises a plurality of chambers 5.

Each chamber 5 can contain a different substance to be electrospun, in order to form a composite fibrous product.

The electrospinning apparatus 1 comprises advantageously voltage regulator means V configured to electrically and independently charge each of said chambers 5 at a different chamber potential, based on the electrical properties of the substance contained in each chamber 5.

Advantageously, the electrospinning apparatus 1 comprises a plurality of heating and/or cooling means 11 configured to heat and/or cool independently each of said chambers 5 to a different desired temperature.

Therefore the voltage in each chamber 5 and the temperature in each chamber 5 can both be controlled and adjusted independently for each chamber 5, based on the electrical, physical and chemical properties of the substance contained in each chamber 5, in order to optimize the electrospinning process of each of the different substances which can be present in the various chambers 5.

Thermo-regulating means T can be provided for activating and controlling the cooling/heating means 11 of each chamber 5, in order to adjust independently the temperature of each chamber 5.

Advantageously each chamber 5 is separated from the other chambers 5 by a non-conductive material, so that the electric field applied to each chamber 5 can be independently modulated without affecting adjacent chambers 5.

The voltage regulator means V comprises a high voltage generator capable of generating a voltage between the chambers 5 and the collector 7.

The high voltage is advantageously comprised in the range between 20 and 200 kV.

Advantageously the electrical field created between the chambers 5 and the collector 7 can be in the range of 2 to 400 kV/m.

A mechanical shutter can be placed below each of the chambers 5 from where the fibers are extruded.

Advantageously the collector 7 comprises, on its top, a film of liquid 19 adapted to collect the fibers extruded through the openings 90 of the forming layer 9. The temperature of the liquid can be controlled.

The liquid can be for example oil or water.

The electrospinning apparatus 1 can also comprise dragging means 23 configured to remove the fibers collected on the film of liquid 19 from said film of liquid 19. The dragging means 23 can be, for example, a roll capable of taking the fibrous material which is being formed on the collector 7.

The electrospinning apparatus 1 can further comprise recirculation means 25 configured to recirculate the liquid of the film of liquid 19 within the collector 7 in order to re-use the liquid.

The recirculation means 25 can comprise a pump.

The film of liquid 19 can be used to obtain hydrophilic-hydrophobic interactions with the extruded fiber so as to improve the dragging, by means of the dragging means 23, of the fibrous material being formed on the collector 7.

Alternatively the collector 7 can comprise, on its top, a solid substrate adapted to collect and entrap the extruded fibers.

The solid substrate can be, for example, agarose, a resin, or a gel-like material.

The solid substrate is capable of entrapping the fibers of the fibrous material which is being formed, in order to stabilize it. The solid substrate can then be removed, after the formation of the fibrous product is completed.

Advantageously the temperature of the collector 7 can also be controlled, preferably by means of the same thermo-regulating means T. Therefore the temperature of the film of liquid 19 or of the solid substrate can also be regulated.

The electrospinning apparatus 1 can comprise cross-linking means 21 adapted to cross-link the fibers collected by the collector 7.

The cross-linking means 21 can comprise a UV light source or other radiation sources.

In addition, the cross-linking means 21 can also comprise heating means or solvent spraying means adapted to improve the stability of the fibrous material which has just been electrospun by chemically or physically crosslinking or stabilizing the fibrous material soon after its formation.

With the present invention it is therefore also possible to spin fibers which are in an unstable stage.

Advantageously the electrospinning apparatus 1 can comprise a tubing system 15 configured to convey the substance to be electrospun to the chambers 5.

Advantageously the distance between the compartment 3 and the collector 7 can be regulated by the operator.

The present invention also regards an electrospinning method, particularly for the production of fibrous materials, comprising the following phases:

-   -   supplying a substance from which fibers are to be formed to at         least one chamber 5 of a compartment 3;     -   electrically charging the at least one chamber 5 at a chamber         potential;     -   electrically charging a collector 7 adapted to collect the         fibers from the at least one chamber 5 at a ground potential         different from the chamber potential, thereby establishing an         electric field between the at least one chamber 5 and the         collector 7.

According to the invention, the substance is extruded into said fibers through a plurality of openings 90 which are present at a forming layer 9 of the at least one chamber 5.

The electrospinning method comprises also the phase of controlling the voltage and the temperature of the chambers 5, each one independently from the other, in order to optimize the electrospinning of the various and different substances which can be present in the chambers 5.

In practice it has been found that the electrospinning apparatus and the electrospinning method according to the present invention achieve the intended aim and objects in that it makes it possible to scale up the production of fibers and fibrous products, and in particular of nanofibers and nanofiber products.

Another advantage of the electrospinning apparatus, according to the invention, consists in that it allows to finely tune the parameters of the electrospinning process, based on the electrical, chemical and physical properties of the substances to be electrospun.

Another advantage of the electrospinning apparatus, according to the invention, consists in that it allows to simultaneously electrospin different polymer melts or solutions, thus obtaining composite fibrous products.

A further advantage of the electrospinning apparatus, according to the invention, consists in that it allows to electrospin also unstable polymer melts or solutions.

The electrospinning apparatus, and the electrospinning method, thus conceived are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements. In practice the materials employed, provided they are compatible with the specific use, and the contingent dimensions and shapes, may be any according to requirements. 

1-12. (canceled)
 13. An electrospinning apparatus, comprising a compartment that comprises at least one chamber adapted to contain a substance from which fibers are to be formed, said at least one chamber being electrically charged at a chamber potential; and a collector adapted to collect said fibers from said at least one chamber, said collector being electrically charged at a ground potential different from said chamber potential, thereby establishing an electric field between said at least one chamber and said collector, wherein said at least one chamber comprises a forming layer comprising a plurality of openings through which said substance is extruded into said fibers.
 14. The electrospinning apparatus according to claim 13, wherein said forming layer is made of an electrically conductive material, said forming layer being electrically charged at said chamber potential.
 15. The electrospinning apparatus according to claim 13, wherein said at least one chamber comprises heating and/or cooling means configured to heat and/or cool said chamber to a desired temperature.
 16. The electrospinning apparatus according to claim 13, further comprising rotation means configured to rotate said compartment with respect to the direction of extrusion of said fibers.
 17. The electrospinning apparatus according to claim 13, wherein said compartment comprises a plurality of said chambers.
 18. The electrospinning apparatus according to claim 17, further comprising voltage regulator means configured to electrically charge independently each of said chambers at a desired different chamber potential.
 19. The electrospinning apparatus according to claim 17, further comprising a plurality of heating and/or cooling means configured to heat and/or cool independently each of said chambers to a different desired temperature.
 20. The electrospinning apparatus according to claim 13, wherein said collector comprises a film of liquid adapted to collect said fibers extruded through said openings of said forming layer.
 21. The electrospinning apparatus according to claim 13, wherein said collector comprises a solid substance adapted to collect and entrap said fibers extruded through said openings of said forming layer.
 22. The electrospinning apparatus according to claim 20, further comprising: dragging means configured to remove said fibers collected on said film of liquid from said liquid; and recirculation means configured to recirculate the liquid of said film of liquid within said collector.
 23. The electrospinning apparatus according to claim 13, further comprising cross-linking means adapted to cross-link said fibers collected by said collector.
 24. An electrospinning method, comprising: supplying a substance from which fibers are to be formed to at least one chamber of a compartment; electrically charging said at least one chamber at a chamber potential; and electrically charging a collector adapted to collect said fibers from said at least one chamber at a ground potential different from said chamber potential, thereby establishing an electric field between said at least one chamber and said collector; and wherein said substance is extruded into said fibers through a plurality of openings which are present at a forming layer of said at least one chamber. 